1. Field of the Invention
The present invention relates to a radio base station device, a radio terminal device and an information communication method for realizing radio communications.
2. Description of the Background Art
Systems for carrying out communications between a radio base station and a radio terminal can be largely classified into a public system in which the radio base station carried out a centralized management of radio bands and a private system in which the radio terminal carries out communications autonomously and radio bands are not managed rigorously.
Conventionally, in the public system, it has been customary to exchange user information through a point-to-point connection between the radio base station and the individual radio terminal.
For example, in the cellular telephone system using TDMA (Time Division Multiple Access) scheme, the radio system manager allocates some time-slot to each radio terminal such that communications between that radio terminal and the radio base station are carried out using only that allocated time-slot.
In such a system, the control methods for carrying out the point-to-point user information communications are defined in advance, and these control methods includes one in which the radio base station broadcasts to a plurality of radio terminals. For example, in the paging for calling up a specific radio terminal, an ID of the radio terminal to be called up and a message containing a command to make the corresponding radio terminal to return a response are broadcast from the radio base station to all radio terminals within an area (called cell) to which radio signals can reach from that radio base station.
Such a conventional radio communication system is provided with means for broadcasting radio control information from the radio base station to all the radio terminals located within the cell of that radio base station. However, the communication involving a radio terminal at least on one side, such as speech communication in the cellular telephone to be specific, has been carried out in the point-to-point fashion, and such a conventional radio communication system has not been provided with any means for transmitting user information from the radio base station to a plurality of radio terminals simultaneously or scheme in which radio terminals receive such user information regardless of whether it is destined to the own terminal or not.
On the other hand, the radio LAN technology that belongs to the private system is compatible with communication systems based on wire Ethernet, and provided with means for each radio terminal or radio base station to transmit information at a variable rate simultaneously with respect to a plurality of radio terminals or a plurality of radio terminals and radio base stations.
In such a system, slots for user information and slots for control information are coexisting without any distinction, or slots with mixed information are existing. For this reason, a receiving device side receives all transmitted information without distinguishing user information and control information, and then judges whether they are destined to the own terminal or not according to the control information among the received information.
However, in this case, contrary to the case of the public system, there is no point-to-point information exchange, and all information must be received once so that there has been a problem that many wasteful processings are involved. Also, in the case where a communication terminal is a mobile terminal with no power supply, there also arises a problem of the power capacity shortage.
As described, it has been impossible to carry out point-to-multipoint user information communications in the conventional radio system of the public system type, whereas it has been impossible to carry out point-to-point user information communications in the conventional radio system of the private system type.